Studies are in progress on the characterization of elastin isolated from histologically defined regions of lung and aorta. Mild extraction procedures have been developed which have led to preparations of elastin with less degradation than those obtained before. A new type of elastin has been isolated from elastic cartilage. Associated with elastin in vascular and pulmonary tissues, one can find, in certain pathological states, deposition of ectopic concretions containing calcium. We have observed the presence of gamma-carboxyglutamic acid in certain of the proteins associated with these calcified areas. Studies are in progress to evaluate the origin and role of these proteins in the calcification mechanism. Initial investigations involve material obtained from the hardened atheromatous plaques associated with human atherosclerosis.